dlloyd:
What precision and accuracy do you need to "measure" the voltage between 100v - 130v DC? (perhaps you should update the thread's title and change "detect" to "measure"). What is the ripple voltage and frequency superimposed on the DC signal, or is there any? What are your thoughts on using a differential amplifier circuit to provide voltage division, subtraction and amplification to output a 0-5V signal (ADC 0-1023) for the 100-130VDC range? Or would it be better to scale the circuit to include some under and over range i.e 90-140VDC?
Well, I will only be using the source voltage measurement to give a rough calculation as to what the duty cycle should start at. This being said, the measurement doesn't have to be terribly precise. With the voltage divider circuit that was suggested by raschemmel, the source voltage is recognized by the arduino board as a number between 0-1023, which represents a voltage of 0 - 140v if I remember correctly. I wanted to only measure between 100-130 because of the more precise measurement than 0 - 140v. However, since there may be instances where the source voltage isn't over 100v like it should be, I think it's actually a good thing that the voltage is being measured all the way from 0-140v. I may actually change the range to 0-160v, just to add a little bit more room for error in the supply voltage.
I appreciate your suggested solution though... as you have now answered the actual question I started this thread for, which nobody had done yet.